Record material for pressure-sensitive copying systems

ABSTRACT

A security feature is imparted to record material for use in pressure-sensitive copying paper systems by dyeing the surface sizing composition and/or other coatings present in the paper and then applying the dyed composition or coating in a manner such as to produce an uneven coating pattern, for example a film-split pattern. The dye accentuates the coating pattern and produces a visual effect which is difficult to replicate without access to a papermaking or paper coating machine, and which has a distinguishably different appearance from that of the opposite surface of the reccord material. The invention is particularly suited for use with a Billblade coater which applies a dyed surface sizing composition to one surface of the paper and a pigment coating to the other surface or with a metered size press coater.

This invention relates to record material for use in pressure-sensitivecopying systems. Such record material is also known as carbonlesscopying paper.

Pressure-sensitive copying systems are well-known and are widely used inthe production of business forms sets. Various types ofpressure-sensitive copying system are known, of which the most widelyused is the transfer type. A business forms set using the transfer typeof pressure-sensitive copying material comprises an upper sheet usuallyknown as a “CB” sheet) coated on its lower surface with microcapsulescontaining a solution in an oil solvent or solvent composition of atleast one chromogenic material (alternatively termed a colour former)and a lower sheet usually known as a “CF” sheet) coated on its uppersurface with a colour developer composition. If more than one copy isrequired, one or more intermediate sheets (usually known as “CFB”sheets) are provided, each of which is coated on its lower surface withmicrocapsules and on its upper surface with colour developercomposition. Imaging pressure exerted on the sheets by writing, typingor impact printing (e.g. dot-matrix or daisy-wheel printing) rupturesthe microcapsules, thereby releasing or transferring chromogenicmaterial solution on to the colour developer composition and giving riseto a chemical reaction which develops the colour of the chromogenicmaterial and so produces a copy image.

In a variant of the above-described arrangement, the solution ofchromogenic material may be present as isolated droplets in a continuouspressure-rupturable matrix instead of being contained within discretepressure-rupturable microcapsules.

In another type of pressure-sensitive copying system, usually known as aself-contained or autogenous system, microcapsules and colour developingco-reactant material are coated onto the same surface of a sheet, andwriting or typing on a sheet placed above the thus-coated sheet causesthe microcapsules to rupture and release the solution of chromogenicmaterial, which then reacts with the colour developing material on thesheet to produce a coloured image.

Business forms sets utilising pressure-sensitive copying materials canbe put to a wide variety of uses in, for example, business, commerce,and national and local government administration. For some of the manyactual or potential uses of these products, it is desirable that atleast one of the sheets making up the set should incorporate a securityfeature of some kind, in order that its authenticity can be verified.This is the case, for example, if one of the sheets of the set is to beused as proof of entitlement to a payment, or example an unemployment,sickness or pension benefit or a refund of tax or customs duty. Suchpayments are often made on presentation of appropriate documentation toa cashier. It is desirable that the cashier should be able to verify theauthenticity of the documentation presented before payment is made.There is therefore a need for pressure-sensitive copying materialincorporating a security feature by means of which its authenticity canbe verified.

In principle, a security feature could be provided in a business formsset by the use of a conventional security paper as the base paper forsubsequent coating with microcapsules and colour developer composition.Such security paper, an example of which is disclosed in our EuropeanPatent Application No. 391542A, can be authenticated by the use of anauthenticating reagent which produces a colour change on application tothe genuine security paper. In practice however, such security papersare normally too expensive for use in business forms sets, except forspecialities such as cheques.

Our European Patent Application No. 0771669A relates to the use offluorescent chromogenic material(s) to provide a security feature inpressure-sensitive copying material. This represents a significantadvance in the art, but there is a market requirement forpressure-sensitive copying systems offering alternative or additionalsecurity features. It is therefore an object of the present invention toprovide pressure-sensitive copying material incorporating acost-effective and readily-verifiable security feature.

We have now discovered that a useful and readily verifiable securityfeature can be obtained if one or more of the coatings used in theproduction of record material for use in pressure-sensitive copyingsystems (including surface sizing coatings) is coloured by the additionof a dye or other colouring agent and then applied to the base papersubstrate by a method which results in a film-split or other unevencoating pattern, i.e. an uneven distribution of the coating over thebase paper surface. This is because the colouring agent has the effectof accentuating the coating pattern. Such coating patterns are difficultto replicate without access to large and expensive paper making and/orcoating equipment. Whereas paper coating technologists normally seek toeliminate or minimise coating patterns, the present invention turns whatis normally a drawback into a benefit.

According to a first aspect of the invention, there is provided recordmaterial for use in pressure-sensitive copying systems, said recordmaterial comprising a paper substrate optionally surfaced-sized with asurface sizing composition and carrying:

(a) a coating of isolated droplets of an oil solution of chromogenicmaterial, said droplets being confined within respectivepressure-rupturable barriers; and/or

(b) a coating of a colour developer material effective to develop thecolour of an oil solution of chromogenic material on contact therewith;

said coatings, when both present, being on opposite surfaces of thesubstrate or on the same surface thereof, and when present on the samesurface being either in separate layers or mixed in a single layer,characterised in that:

(c) at least one of the surface sizing composition, said coatings, or afurther coating carried by the substrate is coloured by the presence ofa dye or other colouring agent and has an uneven coloured coatingpattern, which is accentuated by the colouring agent, the surface of therecord material carrying the coloured coating pattern thus being of adistinguishably different appearance from that of the opposite surfaceof the record material.

In a second aspect, the present invention provides a method of producingrecord material for use in pressure-sensitive copying systems, saidrecord material comprising a paper substrate optionally surface-sizedwith a surface sizing composition and carrying:

(a) a coating of isolated droplets of an oil solution of chromogenicmaterial, said droplets being confined within respectivepressure-rupturable barriers; and/or

(b) a coating of a colour developer material effective to develop thecolour of an oil solution of chromogenic material on contact therewith;

said coatings, when both present, being on opposite surfaces of thesubstrate or on the same surface thereof, and when present on the samesurface being either in separate layers or mixed in a single layer,characterised by the steps of:

(c) adding a dye or other colouring agent to at least one of the surfacesizing composition, said coatings, or a further coating carried by thesubstrate; and

(d) applying and/or smoothing the coloured composition or coating by amethod which results in an uneven coloured coating pattern;

whereby the coating pattern is accentuated by the presence of thecolouring agent and is of a distinguishably different appearance fromthat of the opposite surface of said record material.

In a third aspect, the present invention provides a business forms setcomprising pressure-sensitive copying material as just defined.

The further coating referred to above can be a coating present solelyfor colouration purposes or a coating having an additional technicalfunction, for example, a precoat beneath the coating of isolateddroplets of oil solution.

The surface size, when present, can be conventional in nature, forexample it may be a starch or polyvinyl alcohol surface size.

The pressure-rupturable barrier within which each droplet of chromogenicmaterial solution is confined is typically the wall of a microcapsule.Alternatively, the pressure-rupturable barrier can be part of acontinuous pressure-rupturable matrix as referred to earlier.

The paper substrate may be white or coloured. The hue of the dye orother colouring agent used should differ from the hue of the base paper,and should be such as to be readily noticeable to the human eye.Although it is generally easiest to use a dye as the colouring agent inthe present invention, in principle the colouring agent could takeanother form, for example it could be a particulate coloured pigment(“coloured” in this context includes white) Preferably, the colouringagent is a dye of a type having a strong affinity for cellulosic fibresas used in paper making, so that it will fix to the fibres and not bedisplaced by any subsequent processing.

The colouring agent can be added to a surface sizing formulation, amicrocapsule composition or a colour developer formulation. Theconcentration of colouring agent used can be determined in accordancewith the intensity of pattern desired. Adjustment of colouring agentconcentration to vary the intensity or She pattern obtained can itselfprovide a supplementary security feature. Where the base paper hassizing composition and/or coatings applied to both of its surfaces, thecomposition(s) or coating(s) can both be coloured if desired, providedthe resulting coloured coating patterns are distinguishably different.This will be the case if colouring agents of different hues are used,but the same colouring agent can be used for both surfaces, provided theintensity of colouration and/or the type of coating pattern on the twosurfaces are distinguishably different.

Where the colouring agent is a dye, its degree of affinity forcellulosic paper making fibres is less significant when it is to be usedin the microcapsule coating than when used in a starch surface sizingformulation, since there is less direct contact with the papersubstrate. However, the use of fibre-fixing dyes can still bebeneficial, even in a microcapsule coating.

In one particularly preferred embodiment of the invention, the surfacesizing composition comprising the colouring agent is applied to thesubstrate by means of the roll element of a Billblade coater at the sametime as a colour developer coating is applied to the opposite surface ofthe substrate by means of the blade element of the Billblade coater. Theresult is a CF paper having a distinctive film-split pattern in thesurface size coating which pattern is highlighted and made morenoticeable by the presence of the colouring agent. The distinctivenessof the resulting pattern enhances its value as a security feature. Sincethe result is achieved simply by addition of colouring agent to anotherwise conventional surface sizing composition, achievement of asecurity feature in this way is very cost-effective.

A metered size press coater may be used instead of a Billblade coaterfor applying surface size to one surface of the substrate and a colourdeveloper coating to the opposite surface to produce CF paper. A meteredsize press coater can also be used to produce CB paper if a microcapsulecoating composition is applied to the opposite surface of the substrate,instead of a colour developer coating. Other possibilities offered by ametered size press coater include the application of a precoat asreferred to above to one surface of the substrate and a surface sizingcomposition or colour developer composition to the other surface. Ineach case, the size composition can be coloured, with the CF, CB orprecoat coating uncoloured, or vice versa. Alternatively the surfacesize composition and the CF, CB or precoat coating can both be coloured,provided the colours are different or of distinguishably differentintensities. A metered size press coater can of course also be used justfor surface sizing, i.e. applying the same or different surface sizingcompositions to the opposite surfaces of the base paper substrate, withone or both compositions being coloured (in the latter case, the coloursmust we different or of noticeably different Intensities unless thecoater can be operated to give distinguishably different types ofcoating pattern on the two surfaces). Metered size press coaters arecommercially available from Voith under the name “Speedsizer”; fromValmet under the name “Sym-sizer”; from Jagenberg under the name“Filmpress”; and from BTG under the name “Twin HSM”. Whilst they havebeen designed with a view to eliminating or minimising the occurrence offilm-split or other coating patterns, they can be operated in such wayas to produce a coating pattern sufficient for the purposes of thepresent invention.

A CF product made as described above can readily be made into a CFBproduct by the subsequent application of a suitable microcapsule coatingover the coloured surface size. Since microcapsule coatings are normallytransparent or translucent, the coloured surface size will still bevisible and effective as a security feature.

In another preferred embodiment of the invention, a colouring agent ofdifferent hue to that of the base paper is added to a microcapsulecoating composition prior to its application to the base paper by aroll-coating or other method which produces an uneven coating pattern.As already described in general terms, the effect of the colouring agentis to accentuate irregularities in the evenness with which the coatingis distributed over the surface of the base paper and thus to produce adistinctive coloured pattern.

If desired, the mode of operation of the coating equipment, for examplecoating or smoothing roll speeds, can be modified so as deliberately toobtain a more uneven coating distribution than normal and thereby a moredistinctive coloured pattern. However, our experience is that this isnot normally necessary, as the roll-coating and/or roll-smoothingprocesses conventionally used or coating microcapsules inevitably resultin a “film-split pattern” which is sufficiently distinctive withoutfurther modification.

The present pressure-sensitive copying material may be used not only forapplications in which the material provides proof of entitlement to apayment as described earlier but also for other applications wheresecurity is important. One such application is tickets for sporting ortheatre events or the like or for travel. Another such application isdocuments providing evidence of a right to enter a restricted area orterritory, where entry is granted on presentation of documentaryauthority, for example to a gatekeeper or receptionist or to a border orimmigration official.

When the present record material comprises an oil droplet coating,whether coloured or uncoloured, the chromogenic material present mayinclude a fluorescent component as an additional security feature, asdisclosed in our above-mentioned European Patent Application No. 0771669A.

In other respects, the pressure-sensitive copying material can beconventional. Thus the microcapsules may be produced by coacervation ofgelatin and one or more other polymers, e.g. as described in U.S. Pat.Nos. 2,800,457; 2,800,458, or 3,041,289; or by in situ polymerisation ofpolymer precursor material, e.g. as described in U.S. Pat. Nos.4,001,140; 4,100,103; 4,105,823 and 4,396,670, or by interfacialtechniques such as disclosed in U.S. Pat. Nos. 4,379,071; 4,428,983;4,412,959; 4,253,682; or 4,181,639.

The chromogen-containing microcapsules, once produced, are formulatedinto a coating composition with a suitable binder, for example starch ora starch/carboxymethylcellulose mixture, and a particulate agent (or“stilt material”) for protecting the microcapsules against prematuremicrocapsule rupture. The stilt material may be, for example,wheatstarch particles or ground cellulose fibre floc or a mixture ofthese. The resulting coating composition is then applied by conventionalcoating techniques, for example metering roll coating or air knifecoating.

The thickness and grammage of the base paper used in the present recordmaterial can be as conventional for this type of product, for examplethe thickness may be about 60 to 90 microns and the grammage about 35 to50 g m⁻², or higher, say up to about 100 g m⁻², or even more. Thisgrammage depends to some extent on whether the final paper is for CB,CF, CFB or self-contained use. The higher grammages just quoted arenormally applicable only to speciality CB papers. The base paper may beacid-sized (typically rosin-alum sized) or neutral- or alkaline sized,for example with alkyl ketene dimer or succinic anhydride sizes. Ifneutral- or alkaline-sizing is used, the paper is preferably treatedwith an agent for counteracting discolouration, as disclosed more fullyin our European Patent Application No. 576176A or No. 491487A.

The solvent used to dissolve the chromogenic materials can be chosen,for example, from partially hydrogenated terphenyls, alkyl naphthalenes,diarylmethane derivatives, dibenzyl benzene derivatives, alkyl benzenesand biphenyl derivatives, optionally mixed with diluents or extenderssuch as kerosene, or from vegetable oils, optionally mixed with esters.Such vegetable oil-based systems are disclosed in our European PatentApplications Nos. 520639A, 573210A and 593192A.

The colour developer material used may be an acid clay, e.g. asdescribed in U.S. Pat. No. 3,753,761; a phenolic resin, e.g. asdescribed in U.S. Pat. No. 3,672,935 or U.S. Pat. No. 4,612,254; or anorganic acid or metal salt thereof, e.g. as described in U.S. Pat. No.3,024,927, European Patent Application Nos. 275107A, 503443A or 521474A,or German Offenlegungsschrift No. 4110354A. The colour developermaterial is formulated into a coating composition with a suitablebinder, for example a styrene-butadiene or other latex. The compositionmay of course be coloured to provide the security feature of theinvention.

Additional security features can be incorporated in the present recordmaterial if desired, for example by dyeing the stilt material prior touse or by the inclusion of microcapsules containing coloured dyes. Bothof these expedients produce a coating containing coloured specks visiblewith a hand lens. A further possibility is the inclusion of fluorescentpigment granulates as disclosed in European Patent No. 226367B.

The invention will now be illustrated by the following Examples, inwhich all parts and percentages are by weight unless otherwise stated:

EXAMPLE 1

A fibre-fixing disazo red dye (“Pergasol* Red 2B liquid” supplied byCiba Speciality Chemicals as a wet dye concentrate) was added to twoconventional aqueous starch surface sizing compositions each containing3% by weight of acetylated corn starch (“Collofilm* 124” supplied byAmylum). The concentration of red dye was 0.7% by weight in one batchand 1.4% by weight in the other calculated in both cases as weight ofwet dye concentrate as supplied to total wet weight of surface sizingcomposition.

The resulting dyed solutions were applied separately to one surface of aconventional yellow carbonless base paper by means of the roll elementof a Billblade coater, the blade element of which simultaneously applieda yellow-hue conventional clay-based colour developer composition to theother surface of the paper. In both cases a distinctive and clearlydiscernable red pattern was obtained, with the yellow base paper showingthrough. The higher dye concentration composition gave a much moreintense pattern, and it is probable that with this particular dye, 0.7%is close to the minimum effective dye concentration which could be used.The type of pattern obtained is shown in the accompanying Figure, whichis a photocopy of the coloured pattern obtained, the darker areasrepresenting red and the lighter areas yellow.

Sheets of the resulting papers and of a yellow control CF paper forwhich the surface size had not been dyed red were then laboratory-coatedon their starch-sized surface with a microcapsule composition asconventionally used in carbonless copying paper at a dry coatweight ofca. 5-5.5 g m⁻². This composition contained, on a dry basis, 66% ofmicrocapsules, 24.3% of particulate wheatstarch stilt material and 9.7%of a cooked starch binder. The microcapsules contained a red-developingchromogenic material (“Pergascript* Red I-6B” supplied by Ciba-Geigy)and a fluorescent yellow-developing chromogenic material (“Pergascript*Yellow I-3R”) in 4:1 weight ratio in a 2:1 weight ratio mixture of adi-isopropylnaphthalene blend and kerosene. The microcapsules had beenproduced by a conventional gelatin coacervation microencapsulationprocess as generally described in British Patent No. 870476, usingcarboxymethyl cellulose and vinyl methyl ether/maleic anhydridecopolymer as anionic colloids.

It was observed that the microcapsule coating did not obscure or changethe appearance of the underlying coloured pattern. When the microcapsulecoated surface was illuminated with UV light from a hand-held UV lamp,it was observed that the presence of the underlying coloured pattern didnot interfere with the fluorescence produced by the fluorescentchromogenic material, i.e. it was the same as that obtained with thecontrol paper.

The use of the symbol * in this and subsequent Examples denotes a trademark.

EXAMPLE 2

This illustrates the use of dyed but otherwise conventional microcapsulecompositions to produce patterned CB and CFB products. The dye used wasas in Example 1, and was present in the microcapsule compositions at alevel of 0.3% based on wet dye concentrate as supplied to total dryweight of coating composition. The dyed compositions were applied towhite base paper and to the uncoated surface of yellow CF paper by meansof an intermediate-scale pilot roll coater equipped with aftersmoothingrolls. The web speed of the paper during microcapsule coating was either400 m min⁻¹ or 700 m min⁻¹, and the smoothing rolls were run a variousdifferent speeds so as to achieve a range of coating patterns.

It was found in every case that a distinctive coloured coating patternwas obtained and that the microcapsule-coated surface of the web was ofa distinctively different hue from that of the surface of the web whichwas not microcapsule-coated.

EXAMPLE 3

This illustrates the use of variety of different dyes for colouring themicrocapsule composition. These were all supplied as wet concentratesand were as follows:

A. “Astrazon* Blue FBL” (an azacyanine liquid dyestuff preparationsupplied by Bayer and containing 30-40% C.I. Basic Blue 159) used ataddition levels of 0.25%, 0.5% and 1.0%.

B. “Levacell* FT Blue 4G-N (an azo copper complex dyestuff preparationbased on bis-diazotised 3,3′-methoxybenzidene, supplied by Bayer andcontaining 20% C.I. Direct Blue 218), used at addition levels of 0.5%and 1.0%.

C. Mixture of “Pergasol* Turquoise F-2G” (a phthalocyanine liquiddyestuff preparation supplied by Ciba Speciality Chemicals andcontaining C.I. Basic Blue 100) and “Levacell* Fast Yellow GF-N” (an azoliquid dyestuff preparation supplied by Bayer and containing C.I. DirectYellow 147) in approximately 1:1 proportion.

D. Mixture of “Levacell* Fas yellow GF-N” and “Pergasol* Turquoise F-2G”in approximately 1:2 proportion.

E. “Pergasol* Red 2B” used at addition levels of 0.5%, 1.0% and 2.7%.

The various dyed microcapsule compositions were applied to he uncoatedsurface of yellow 57 g m⁻² CF paper by means of a small scale pilot rollcoater. In all cases, distinctive coating patterns were obtained,although those obtained with “Astrazon Blue FBL” were less distinctivethan the others.

EXAMPLE 4

An aqueous coating composition for use as a precoat beneath amicrocapsule coating in pressure-sensitive record material was made upat 46.2% solids content from the following:

Kaolin (“SPS”* supplied by 100 parts (dry) English China Clays, UnitedKingdom) Oxidised potato starch binder 20 parts (dry) (“Perfectamyl*P255 SH supplied by Amylum N.V., Belgium) Cyclic amide-aldehydecondensate 1 part (dry) cross-linking agent (“Sunrez 700M*, product ofSequa Chemicals Inc. USA)

50 ml of red dye concentrate (“Pergasol* Red 2B”) was added to 70 Kg ofaqueous coating composition prepared as just described (this representsca. 155 g of dye concentrate per 100 Kg dry coating composition).

The resulting dyed composition was then applied to one surface of aconventional white base paper at a dry coatweight of ca. 4.7 g m⁻² bymeans of a pilot scale blade coater. The coater was operated in a mannersuch as not to avoid the occurrence of a coating pattern. The resultingpaper had a pinkish appearance on the coated surface, but was white onthe reverse. On examination of the pink surface with the naked eye, itwas found to comprise a subtle but clearly discernible red-on-whitemottle pattern in which the dye accentuated the coating pattern. Thecoating pattern was not readily discernable on a control paper coated inthe same way with an undyed coating composition which was otherwiseidentical to that described above. When a microcapsule composition isapplies over the red-on-white mottle pattern and dried, the pattern isstill visible through the microcapsule coating.

EXAMPLE 5

This illustrates the use of a metered size press coater (pilot-scale)for applying a conventional clay-based colour developer composition toone surface of a white base paper and an inert kaolin pigment precoatcomposition to the other surface (the precoated surface was intendedsubsequently to be coated with a microcapsule composition). The precoatwas coloured blue by the addition of blue dye at a level of ca. 0.125 Kgdye per 100 Kg coating composition on a dry basis. The resulting coatedpaper was white on one surface (the CF surface) and generally blue onthe other surface, the blue surface having a noticeable mottled coatingpattern with the white base paper showing through.

EXAMPLE 6

This also illustrates the use of a pilot-scale metered size press coaterfor applying a conventional clay-based colour developer composition toone surface of a white base paper and an inert kaolin pigment precoatcomposition to the other surface. However, in contrast to Example 5,both compositions were coloured blue by the addition of blue dye(addition level 0.5 Kg of dye per 100 Kg coating composition on a drybasis in each case). The resulting coated paper was blue on bothsurfaces but the coating patterns on the surfaces were noticeablydifferent (the coating pattern on the colour developer surface was morepronounced than on the precoat surface). In each case the white basepaper showed through on close examination.

What is claimed is:
 1. Record material for use in pressure-sensitivecopying systems, said record material comprising a paper substrateoptionally surfaced-sized with a surface sizing composition andcarrying: (a) a coating of isolated droplets of an oil solution ofchromogenic material, said droplets being confined within respectivepressure-rupturable barriers; and/or (b) a coating of a colour developermaterial effective to develop the colour of an oil solution ofchromogenic material on contact therewith; said coatings, when bothpresent, being on opposite surfaces of the substrate or on the samesurface thereof, and when present on the same surface being either inseparate layers or mixed in a single layer, characterised in that: (c)at least one of the surface sizing composition, or said coatings iscoloured by the presence of a dye or other colouring agent and isapplied and/or smoothed by a method which results in an uneven colouredcoating pattern, whereby the coating pattern is accentuated and thesurface of the record material carrying the coloured coating pattern isof a distinguishably different appearance from that of the oppositesurface of the record material.
 2. Record material as claimed in claim1, wherein the coating having the uneven coloured coating pattern is ofa surface sizing composition containing a colouring agent.
 3. Recordmaterial as claimed in claim 1, wherein the coating having the unevencoloured coating pattern is of a microcapsule coating compositioncontaining a colouring agent.
 4. Record material as claimed in claim 1wherein the coating having the uneven coloured coating pattern is of acolour developer composition containing a colouring agent.
 5. Recordmaterial as claimed in claim 1 wherein the colouring agent is a dye of atype having a strong affinity for cellulosic fibres, so that it fixes tothe fibres of the paper substrate.
 6. Record material as claimed inclaim 1 wherein the chromogenic material includes a fluorescentcomponent.
 7. A business forms set comprising pressure-sensitive copyingmaterial as claimed in claim 1.